As a conventional acousto-electric transducer using light (hereinafter referred to as an optical-acoustic transducer), there is known an optical-acoustic transducer shown in FIG. 13, in which a plane diaphragm 11 is fixed to a frame 4 via a ring 3, a light emitter 5 and a light receiver 6 are further fixed to the frame 4, and light irradiated from the light emitter 5 and reflected at the diaphragm 11 is received at the light receiver 6, whereby a position of the diaphragm 11 namely, a vibration is converted into an electric signal.
In an optical acoustic transducer shown in FIG. 13, a diaphragm is flat, and therefore compliance of the diaphragm 11 cannot be made large. To eliminate the disadvantage, in a conventional optical-acoustic transducer shown in FIG. 14, the cross section of the part from the center of a diaphragm 12 to a perimeter portion is formed in a corrugated form so that a valley and a peak are formed, the perimeter portion is fixed to the frame 4, and the light emitter 5 and the light receiver 6 are fixed to the frame 4.
In a conventional optical-acoustic transducer shown in FIG. 15, a dome-shaped reflecting portion 13a is provided at a center of a diaphragm 13, corrugation is formed from the reflecting portion 13a to a perimeter portion, a supporting portion 13b provided at the perimeter portion is fixed to the frame 4, and the light emitter 5 and the light receiver 6 are fixed to the frame 4.
In order to reduce the optical-acoustic transducers in size and transduce sound with high sensitivity, it is necessary to reduce the diaphragms in size and increase compliance. An optical-acoustic transducer, which is proposed in Japanese Patent Application No. 2001-184530 in response to the requirement, is shown in FIG. 16 and FIG. 17.
Namely, an optical-acoustic transducer using a diaphragm 14, which is provided with a dome-shaped reflecting portion 14a at a center and a corrugation between the reflecting portion 14a and a supporting portion 14b, is further improved by cutting predetermined spots of the diaphragm 14 with laser light or the like to form arc-shaped slits 15a and spiral slits 15b. 
The supporting portion 14b of the diaphragm 14 is fixed to the frame 4. Though the illustration of a light emitter and a light receiver is omitted in FIG. 16 and FIG. 17, the light emitter and the light receiver are fixed to the frame as in the above-described prior arts. The spiral slits 15b and the arc-shaped slits 15a construct cantilevers 14c, 14c, . . . , and a substantially maximum outer side portion of a vibrating section, whereby amplitude performance of the diaphragm 14 is improved and performance of the optical-acoustic transducer is enhanced.
However, it is obvious that the optical-acoustic transducers in these days have extremely increasing requirement for reduction in size, and to respond to the requirement for size reduction, the diameter of the vibration plate 14 formed in the dome shape as shown in FIG. 16 cannot help being made small. Since part of the vibrating plate 14 is cut in this example, the proportion occupied by the cantilever area is increased and the area of the diaphragm 14 is reduced as the diameter of the diaphragm 14 becomes smaller, and as a result, it cannot be denied that the structure of this diaphragm is such that an air pressure receiving area cannot help being reduced.
The aforementioned Japanese Patent Application No. 2001-184530 describes that it is preferable to provide a rib structure at an outer side portion of the adjacent vibrating section when suspension of the cantilevers 14c is provided at part of the diaphragm 14, but the shape of the diaphragm 14 becomes a complicated three-dimensional structure, and as a matter of course, there arises the problem that the production cost of the forming die and the like of the diaphragm 14 tends to be high.